Placing buffs on mines will always have two results, either the mine runs dry before the buff has ended or the buff ends before the mine runs dry. With a mine buff bank you can use buff time that you have collected from adventure loot or bought from the merchant etc and set your own time on how long the buff will run for. It would be just like collecting deposit in your star menu and used in the same way. Then any buff time that remains after the mine runs dry goes back into your star menu. There could be +100%, +200% or even +300% buff time.
Buff name: Buff Time
Buff image: